In communication networks, such as networks based on Long Term Evolution, LTE, as specified by the Third Generation Partnership Project, 3GGP, there are certain data layer functions designed for mass communication with a large number of wireless devices, referred to as “user equipments” or UEs in the 3GPP lexicon. In particular, some data layer functions are designed for peer-to-peer control of transport channels and for the mapping between transport channels and logical channels. Example functions include those used by the Radio Resource Control, RRC, protocol and the Medium Access Control, MAC, sublayer in 3GPP LTE.
According to the Evolved Packet System or EPS defined by the 3GPP LTE architecture, the radio access network is referred to as an Evolved Universal Terrestrial Radio Access Network, or E-UTRAN. The E-UTRAN includes base stations, referred to as eNodeBs or eNBs that provide E-UTRA user-plane and control-plane protocol terminations towards the UEs. User-plane protocol examples include Packet Data Convergence Protocol or PDCP, Radio Link Control or RLC, MAC, and Physical Layer or PHY, while control-plane protocol examples include RRC.
The eNBs are connected by means of an “S1” interface to core network, which is referred to as an Evolved Packet Core or EPC. More specifically, the eNBs have S1 connections to a Mobility Management Entity, MME, through an S1-MME interface and to a Serving Gateway, S-GW, through an S1-U interface. Upon request from an MME, an eNB performs an E-RAB to radio bearer mapping and establishes a Data Radio Bearer and allocates the required resources on the air interface, referred to as the “Uu” interface. The eNB also sets up a logical channel for the UE and allocates it to a transport channel. These operations involve the MAC layer.
3GPP specifies the E_UTRAN MAC protocol as a sub layer of layer 2. Functions of the MAC sub layer are performed by MAC entities in the UE and in the E-UTRAN. For a MAC entity configured at the eNB, there is a peer MAC entity configured at the UE and vice versa.
The mapping of logical channels to transport channels at the MAC sublayer is configured by RRC. There is one Logical Channel Identifier, LCID, field for each MAC service data unit, SDU, included in the corresponding MAC protocol data unit, PDU. The LCID field size is 5 bits, where the values 00000 and 01011 are reserved for CCCH and the value 11111 is reserved for padding. The LCID for the Downlink Shared Channel, DL-SCH, uses the range 11011- 11110 for MAC Control Elements, MAC CEs. A MAC CE is an explicit MAC inband control message. The range 01011-11001 is reserved for future needs within the framework of the controlling standard. Similarly, the LCID for the Uplink Shared Channel, UL-SCH, uses the range 11000-11110 for explicit MAC inband control, while the range 01100-10111 is reserved for future needs within the standard.
Further, the LCID values that are predefined for use in identifying logical channels in the MAC sublayer is 00001-01010. From within this range, the LCID values of 00001 and 00002 are reserved for the signaling radio bearers used by RRC. Consequently, there are eight LCID values available for mapping logical channels to data radio bearers.
These and other details can be seen in the below tables, excerpted from 3GPP TS 36.321,V12.4.0 (2015-01). In particular, FIG. 1 depicts “Table 6.2.1-1 Values of LCID for DL-SCH”, FIG. 2 depicts “Table 6.2.1-2 Values of LCID for UL-SCH”, FIG. 3 depicts “Table 6.2.1-3 Values of F field”, and FIG. 4 depicts “Table 6.2.1-4 Values of LCID for MCH”.
From the above information and excerpted tables, one sees that in the example context of LTE, there is a relatively scarce range of LCID values within the predefined set(s) of LCID values. Moreover, one sees that the standard tightly controls the meaning and use of the LCID values. As a general proposition, conformance to these default meaning or mappings is required for proper operation between the network and the wireless devices. Moreover, to the extent that one might wish to deviate from or expand these default mappings, standardizing new LCIDs for MAC control or other purposes is a slow, cumbersome process.